Method and apparatus for combined cycle power plant startup

ABSTRACT

A combined cycle power plant startup system is provided. The system includes a steam turbine, a HRSG, a condenser, and a bypass system. The steam turbine may include a turbine section. The HRSG may be operably connected to the steam turbine for providing steam to the steam turbine. The HRSG may include a reheater. The bypass system may be configured to adjust the steam pressure downstream of the reheater by routing steam downstream of the reheater to the condenser. The bypass system may include at least one bypass line, at least one control valve operably connected to the at least one bypass line, a pressure gauge configured to monitor the steam pressure downstream of the reheater, and a controller configured to communicate with the pressure gauge and operate the at least one control valve.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to combined cyclepower plants, and more specifically to methods and apparatus for startupof a combined cycle power plant.

BACKGROUND OF THE INVENTION

A conventional combined cycle power plant generally includes one or moregas turbines, heat recovery steam generators (“HRSG's”), and a steamturbine. Because excessive steam pressures generated when the gasturbine is operating at high- or full-load can stress steam turbinecomponents during steam turbine startup, traditional combined cyclepower plant startup procedures require placing low load holds on the gasturbines and placing restrictions on gas turbine loading rates tocontrol steam pressure during steam turbine startup.

Such holds and restrictions contribute to high gas turbine exhaustemissions during startup, increased startup and loading times, andincreased fuel consumption during startup and loading. Thus, by holdinggas turbines at low loads and loading rates, the gas turbines are forcedto operate at low efficiency with high exhaust emissions during steamturbine startup and loading. Further, low gas turbine loads and loadingrates cause the revenues generated by combined cycle power plants to belower during steam turbine startup and loading.

Various strategies are known in the art for providing combined cyclepower plant startup procedures which allow gas turbines and HRSG's to beoperated under normal operating conditions during steam turbine startupand loading. For example, one strategy is to include additional pipingand valves in combined cycle power plants, to lower steam pressuresprior to admission to the steam turbine by routing excess steam toequipment designed to contain the steam, such as to a condenser.However, the addition of piping to a combined cycle power plant isexpensive. Additionally, the space available for additional piping in acombined cycle power plant may be limited, and the installation ofadditional piping may be difficult. Further, the configuration ofadditional piping in a combined cycle power plant may cause large,uncontrollable pressure drops, which can damage the power plant.

Thus, an improved system and method for combined cycle power plantstartup is desirable in the art. For example, a system and method forrouting steam flow during steam turbine startup and loading, to lowersteam pressures prior to admission to the steam turbine while allowinggas turbines and HRSG's to operate under normal operating conditionswould be advantageous. Additionally, a combined cycle power plantstartup system that uses existing power plant piping may be desirable.Further, a combined cycle power plant startup system that isinexpensive, easy to install, and controllable under all power plantoperating conditions would be accepted in the art.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one embodiment, a combined cycle power plant startup system isprovided that includes a steam turbine, a HRSG, a condenser, and abypass system. The steam turbine may include a turbine section. The HRSGmay be operably connected to the steam turbine for providing steam tothe steam turbine. The HRSG may include a reheater. The bypass systemmay be configured to adjust the steam pressure downstream of thereheater by routing steam downstream of the reheater to the condenser.The bypass system may include at least one bypass line, at least onecontrol valve operably connected to the at least one bypass line, apressure gauge configured to monitor the steam pressure downstream ofthe reheater, and a controller configured to communicate with thepressure gauge and operate the at least one control valve. The steampressure may thus be adjusted to a pressure range suitable for admissionto the turbine section.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedFIGURE, in which:

FIG. 1 provides a schematic diagram of one embodiment of the combinedcycle power plant startup system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

FIG. 1 is a schematic diagram of one embodiment of a combined cyclepower plant startup system 10. The system 10 may include a gas turbine(not shown), a steam turbine 12, a heat recovery steam generator(“HRSG”) 14, and a condenser 16. For example, the HRSG 14 and thecondenser 16 may be operably connected to the steam turbine 12. Further,the system 10 may include more than one gas turbine, steam turbine 12,HRSG 14, and condenser 16.

The steam turbine 12 may include a turbine section 18. For example, inone embodiment, the turbine section 18 may be an intermediate pressureturbine. The steam turbine 12 may further include other turbine sectionssuch as, for example, turbine sections 17 and 19. For example, in oneembodiment, turbine section 17 may be a low pressure turbine. In oneembodiment, turbine section 19 may be a high pressure turbine. The steamturbine 12 may further include other turbine sections. It should beunderstood that the turbine sections 17, 18 and 19 of the presentdisclosure are not limited to low pressure, intermediate pressure andhigh pressure turbines, but may be any turbine, turbine section, orturbine component that is operable in a steam turbine.

The HRSG 14 may include a first drum section 41, a second drum section42, and a reheater 15. The first drum section 41 and second drum section42 may be configured to provide steam to various components of thesystem 10. For example, in one embodiment, the first drum section 41 maybe a high pressure drum section, which may be coupled with a downstreamsuperheater section (not shown). The high pressure drum section andsuperheater section may supply superheated steam at a high pressure. Thesteam supplied by first drum section 41 may be routed to a turbinesection, such as to turbine section 19. A control valve 46 may beconfigured to control the supply of steam to the turbine section 19.Further, the steam may be routed to a bypass system 45 when, forexample, the turbine section 19 is offline. The bypass system 45 may be,for example, a cascading bypass system. After passing through turbinesection 19 and bypass system 45, the steam may then be routed to thereheater 15.

In an exemplary aspect of an embodiment, the second drum section 42 maybe an intermediate pressure drum section, and the intermediate pressuredrum section may supply steam at an intermediate pressure. The steamsupplied by second drum section 42 may be routed to the reheater 15.Further, in one embodiment, the steam supplied by second drum section 42may be combined with the steam downstream of the turbine section 19 andthe bypass system 45 before the steam is admitted to the reheater 15.

The reheater 15 may be configured to heat steam supplied by variouscomponents of system 10 before the steam is admitted to turbine section18. For example, steam downstream of first drum section 41, turbinesection 19, bypass system 45, and second drum section 42 may be admittedto the reheater 15 through reheater inlet 15.1. This steam may be heatedin the reheater 15, such as to a hot reheat steam temperature, beforethe steam is admitted to the pressure turbine 18. A control valve 47 maybe configured to control the supply of steam to the turbine section 18.

Thus, in an exemplary aspect of an embodiment, under normal operatingconditions, the first drum section 41 of the HRSG 14 may supply steam tothe turbine section 19 of the steam turbine 12. The steam may be at arelatively high pressure, and the first drum section 41 and the turbinesection 19 may be a high pressure drum section and a high pressureturbine, respectively. For example, in one embodiment, the steam may besupplied from the first drum section in a range from approximately 1800to approximately 2500 pounds per square inch atmospheric (“psia”), orany subrange therebetween.

After energy is extracted from the steam by the turbine section 19, thesteam may then be supplied to the reheater 15 for reheating. In oneembodiment, before the steam enters the reheater 15 through reheaterinlet 15.1, the steam may be combined with steam supplied by the seconddrum section 42 of the HRSG 14. The steam supplied by the second drumsection 42 may be at a relatively intermediate pressure, and the seconddrum section 42 may be an intermediate pressure drum section. Forexample, in one embodiment, the steam may be supplied from the seconddrum section in a range from approximately 100 to approximately 380psia, or any subrange therebetween.

The steam downstream of the first drum section 41, turbine section 19,bypass system 45, and second drum section 42 may then enter the reheater15 through the reheater inlet 15.1. The reheater 15 may be configured toheat the steam before the steam is admitted to turbine section 18, suchas to a hot reheat steam temperature. Under normal operating conditions,after the steam is heated by the reheater 15, the steam may then besupplied to the turbine section 18. The steam downstream of the reheater15 may be at a relatively intermediate pressure, and the turbine section18 may be an intermediate pressure turbine. In one embodiment, the steamdownstream of the reheater 15 may be supplied from the reheater 15 at apressure exceeding 120 psia. For example, under normal operatingconditions, the steam downstream of the reheater 15 may be supplied fromthe reheater 15 in a range from approximately 250 to approximately 380psia, or any subrange therebetween.

After energy is extracted from the steam in the turbine section 18, thesteam may be supplied to the turbine section 17. The steam supplied bythe turbine section 18 may be at a relatively low pressure, and theturbine section 17 may be a low pressure turbine. For example, in oneembodiment, the steam may be supplied from the turbine section 18 to theturbine section 17 in a range from approximately 15 to approximately 60psia, or any subrange therebetween.

After energy is extracted from the steam in the turbine section 17, thesteam may be supplied to the condenser 16. The condenser 16 may operateto condense the steam, which may then be supplied back to the system 10.

It should be understood that the pressure ranges disclosed for thenormal operating conditions of the turbine sections 17, 18 and 19, thefirst and second drum sections 41 and 42, and the reheater 15 are merelyillustrative of the normal operating conditions of a combined cyclepower plant. Operation of the turbine sections 17, 18 and 19, the firstand second drum sections 41 and 42, and the reheater 15 are not limitedto those pressure ranges disclosed. Rather, the turbine sections 17, 18and 19, the first and second drum sections 41 and 42, and the reheater15 may be operated in any pressure ranges known in the steam turbineart.

The system 10 may further include attemperators 48 and 49. In oneembodiment, attemperator 48 may be configured to cool steam as it exitsthe bypass system 45. In one embodiment, attemperator 49 may beconfigured to cool steam before it enters the condenser 16.

The system 10 may further include a first bypass system 20. The firstbypass system 20 may be configured to adjust the pressure of steamdownstream of the reheater 15 by routing steam downstream of thereheater 15 to the condenser 16. For example, in one embodiment, thefirst bypass system 20 may be an intermediate pressure bypass system.Routing stream downstream of the reheater 15 to the condenser 16 mayadjust the pressure of the steam downstream of the reheater 15 to apressure range suitable for admission to the turbine section 18.

In an exemplary aspect of an embodiment, the first bypass system 20 maybe configured to adjust the pressure of steam downstream of the reheater15 to a pressure range suitable for startup of the turbine section 18.In another exemplary aspect of an embodiment, the first bypass system 20may be configured to adjust the pressure of steam downstream of thereheater 15 to a pressure range suitable for shutdown of the turbinesection 18. For example, in one embodiment, the pressure ranges suitablefor startup and shutdown of the turbine section 18 are the same. Inanother embodiment, the pressure range suitable for startup of theturbine section 18 is different from the pressure range suitable forshutdown of the turbine section 18. In one embodiment, startup orshutdown of the turbine section 18 may occur while the gas turbine andthe HRSG 14 are operating at normal operating conditions.

For example, in an exemplary aspect of an embodiment, the turbinesection 18 may be an intermediate pressure turbine. The pressure rangeof steam that may be suitable for admission to the intermediate pressureturbine, such as, for example, for startup or shutdown of theintermediate pressure turbine, may be from approximately 90 toapproximately 120 psia, or any subrange therebetween. The pressure ofthe steam downstream of the reheater 15 may, for example, exceed 120psia. For example, under normal operating conditions, steam downstreamof the reheater 15 may be supplied from the reheater 15 in a range fromapproximately 250 to approximately 380 psia, or any subrangetherebetween. Thus, the first bypass system 20 may be configured toadjust the pressure of the steam downstream of the reheater 15 fromabove 120 psia to a range of from approximately 90 to approximately 120psia, which may be a pressure range suitable for startup or shutdown ofthe intermediate pressure turbine. It should be understood, however,that the steam pressure ranges suitable for admission to the turbinesection 18 are not limited to the range from 90 to 120 psia, and may beany steam pressure ranges desired in a turbine section 18, steam turbine12 or system 10.

The first bypass system 20 may include at least one bypass line 21 andat least one control valve 22. Further, in one embodiment, the at leastone bypass line 21 may be a plurality of bypass lines 21, and the atleast one control valve 22 may be a plurality of control valves 22. Thecontrol valves 22 may be operably connected to the bypass lines 21.

The first bypass system 20 may further include a controller 23 and apressure gauge 24. The pressure gauge 24 may be operably connected tothe controller 23. The pressure gauge 24 may be configured to monitorthe pressure of steam downstream of the reheater 15. The controller 23may be configured to communicate with the pressure gauge 24 and operatethe control valves 22, such that the first bypass system 20 operates toadjust the pressure of steam downstream of the reheater 15 to a pressurerange suitable for admission to the turbine section 18.

For example, in an exemplary aspect of an embodiment, the controller 23may be configured to operate the control valves 22 in sequence. Inanother exemplary aspect of an embodiment, the controller 23 may beconfigured to operate the control valves 22 in tandem. It should beunderstood, however, that the configuration of the controller 23 tooperate the control valves 22 is not limited to operation of the controlvalves 22 in sequence or in tandem, but may be any configurationdesigned to adjust the pressure of steam downstream of the reheater 15.

In an exemplary aspect of an embodiment, the controller 23 may beconfigured to operate the control valves 22 in sequence. For example,operating the control valves 22 in sequence may include opening thecontrol valves 22 when steam downstream of the reheater 15 reaches afixed pressure limit, setting a first control valve 22.1 toauto-control, and setting a second control valve 22.2 to auto-controlwhen the first control valve 22.1 reaches a fixed valve stroke limit. Inone embodiment, the step of opening the control valves 22 may includesetting the control valves 22 at a minimum stroke setting. In oneembodiment, the step of setting a control valve 22 to auto-control mayinclude setting the control valve 22 at an adjustable stroke setting,such that the stroke of the control valve 22 automatically adjusts inorder to adjust or maintain the pressure of steam downstream of thereheater 15 at a pressure range suitable for admission to the turbinesection 18. Further, the step of setting a second control valve toauto-control when a first control valve reaches a fixed valve strokelimit may be repeated in sequence for multiple control valves 22. Itshould be understood that the control valves 22 are not limited to afirst control valve 22.1 and a second control valve 22.2, but mayinclude any number of control valves 22 necessary to adjust the pressureof steam downstream of the reheater 15.

For example, in an exemplary aspect of an embodiment, the pressure gauge24 of the first bypass system 20 may sense that the pressure of thesteam downstream of the reheater 15 is at a pressure exceeding a fixedpressure limit. The pressure gauge 24 may communicate this condition tothe controller 23. The controller 23 may then operate the control valves22 by opening the control valves 22 to a minimum stroke setting andsetting a first control valve 22.1 to auto-control. The stroke of thefirst control valve 22.1 may thus automatically adjust, to adjust ormaintain the pressure of the steam downstream of the reheater 15 in apressure range suitable for admission to the turbine section 18, untilthe stroke of the first control valve 22.1 reaches a fixed valve strokelimit. If the first control valve 22.1 reaches the fixed valve strokelimit, the controller 23 may operate to set a second control valve 22.2to auto-control. If the second control valve 22.2 reaches the fixedvalve stroke limit, the controller 23 may operate to set another controlvalve 22 to auto-control, and this sequence may be repeated for multiplecontrol valves 22. This procedure may be followed to adjust the pressureof steam downstream of the reheater 15 to a pressure range suitable foradmission to the turbine section 18, such as to a pressure rangesuitable for startup or shutdown of the turbine section 18.

In one embodiment, the fixed pressure limit may be 120 psia. In oneembodiment, the fixed valve stroke limit may be 90%. In anotherembodiment, the fixed valve stroke limit may be 100%. In yet anotherembodiment, the fixed valve stroke limit may be a range from 90% to100%, or any subrange therebetween.

In an exemplary aspect of an embodiment, the first bypass system 20 maybe constructed at least partially from existing combined cycle powerplant equipment. For example, existing combined cycle power plantcomponents may be rerouted, converted, or modified to construct thefirst bypass system 20. In one embodiment, various bypass lines 21 andcontrol valves 22 of the first bypass system 20 may be constructed fromexisting combined cycle power plant equipment. In one embodiment,control valve 22.1, its associated bypass line 21, and controller 23 maybe constructed from existing combined cycle power plant equipment. Forexample, control valve 22.1, its associated bypass line 21, andcontroller 23 may be rerouted, converted, or modified for use in thefirst bypass system 20. The use of existing equipment to construct thefirst bypass system 20 may be advantageous, as the use of existingequipment may make the first bypass system 20 inexpensive to install,and may allow the first bypass system 20 to be installed within limitedspace requirements. Further, the limited use of additional piping may,for example, prevent large, uncontrollable pressure drops, which coulddamage the power plant. It should be understood that the existingcombined cycle power plant equipment of the present invention is notlimited to bypass lines 21 or control valves 22, but may be any combinedcycle power plant equipment that could be used to construct the bypasssystem 20.

In one embodiment, the combined cycle power plant startup system 10 mayinclude a second bypass system 30. The second bypass system 30 may beconfigured to adjust the pressure of steam upstream of the reheater 15by routing steam upstream of the reheater 15 to the first bypass system20. In one embodiment, the second bypass system 30 may be configured toroute steam from the first drum section 41 to the first bypass system20. In one embodiment, the second bypass system 30 may be configured toroute steam through the first bypass system 20 to the condenser 16. Inan exemplary aspect of an embodiment, the second bypass system 30 may bea high pressure bypass system.

For example, routing steam upstream of the reheater 15 to the firstbypass system 20 may adjust the pressure of the steam at the reheaterinlet 15.1. Adjusting the pressure of the steam at the reheater inlet15.1 may adjust the temperature of the steam exiting the turbine section19. For example, lowering the pressure of the steam at the reheaterinlet 15.1 may lower the temperature of the steam exiting the turbinesection 19. Adjusting the temperature of the steam exiting the turbinesection 19 may reduce the strain on the system 10.

Further, routing steam upstream of the reheater 15 to the first bypasssystem 20 may adjust the pressure of the steam upstream of the turbinesection 19 and the control valve 46. Adjusting the pressure of the steamupstream of the turbine section 19 and control valve 46 may adjust thepressure drop across the control valve 46. For example, lowering thepressure of the steam upstream of the turbine section 19 and controlvalve 46 may lower the pressure drop across the control valve 46.Adjusting the pressure drop across the control valve 46 may increase thereliability and longevity of the control valve 46.

The second bypass system 30 may include at least one bypass line 31 andat least one control valve 32. Further, in one embodiment, the at leastone bypass line 31 may be a plurality of bypass lines 31, and the atleast one control valve 32 may be a plurality of control valves 32. Thecontrol valves 32 may be operably connected to the bypass lines 31.

The second bypass system 30 may further include a controller 33 and apressure gauge 34. The pressure gauge 34 may be operably connected tothe controller 33. The pressure gauge 34 may be configured to monitorthe pressure of the steam upstream of the reheater 15. The controller 33may be configured to communicate with the pressure gauge 34 and operatethe control valves 32, such that the second bypass system 30 operates toadjust the pressure of steam upstream of the reheater 15. For example,in one embodiment, the controller 33 may be configured to operate thecontrol valves 32, such as, for example, operating the control valves 32in tandem or in sequence, as discussed above regarding the first bypasssystem 20, when steam upstream of the reheater 15 reaches a fixedpressure limit. For example, in one embodiment, the controller 34 mayoperate the control valves 32 by opening the control valves 32 to aminimum stroke setting and sequentially setting the control valves 32 toauto-control when the control valves 32 reach a fixed valve strokelimit, as discussed above regarding the first bypass system 20. In oneembodiment, the controller 33 may be configured to operate the controlvalves 32 when steam immediately upstream of reheater inlet 15.1 reachesa fixed pressure limit.

For example, in an exemplary aspect of an embodiment, the pressure gauge34 may sense that the pressure of steam upstream of the reheater 15,such as immediately upstream of reheater inlet 15.1, is at a pressureexceeding a fixed pressure limit. The pressure gauge 34 may communicatethis condition to the controller 33. The controller 33 may then operateto open the control valves 32 and sequentially set the control valves 32to auto-control, as discussed above regarding the first bypass system20.

In one embodiment, the fixed pressure limit may be 130 psia. In oneembodiment, the fixed valve stroke limit may be 90%. In anotherembodiment, the fixed valve stroke limit may be 100%. In yet anotherembodiment, the fixed valve stroke limit may be a range from 90% to100%, or any subrange therebetween.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A combined cycle power plant startup system comprising: a steam turbine, the steam turbine comprising a turbine section; a heat recovery steam generator operably connected to the steam turbine for providing steam to the steam turbine, the heat recovery steam generator comprising a reheater; a condenser; and a bypass system configured to adjust the steam pressure downstream of the reheater by routing steam downstream of the reheater to the condenser, the bypass system comprising a plurality of bypass lines, a plurality of control valves operably connected to the plurality of bypass lines, a pressure gauge configured to monitor the steam pressure downstream of the reheater, and a controller programmed to communicate with the pressure gauge and operate the plurality of control valves in sequence, wherein operating the plurality of control valves in sequence comprises opening the plurality of control valves when steam downstream of the reheater reaches a fixed pressure limit, setting a first control valve to auto-control, and setting a second control valve to auto-control when the first control valve reaches a fixed valve stroke limit, and wherein setting one of the first control valve or the second control valve to auto-control comprises setting the control valve to an adjustable stroke setting, such that a stroke of the control valve automatically adjusts in order to adjust or maintain the pressure of steam downstream of the reheater at a pressure range suitable for admission to the turbine section, the steam pressure being adjusted to a pressure range suitable for admission to the turbine section.
 2. The combined cycle power plant startup system of claim 1, wherein the turbine section is an intermediate pressure turbine.
 3. The combined cycle power plant startup system of claim 1, wherein the fixed pressure limit is about 120 pounds per square inch atmospheric.
 4. The combined cycle power plant startup system of claim 1, wherein the fixed valve stroke limit is about 90%.
 5. The combined cycle power plant startup system of claim 1, wherein the steam pressure is adjusted to a pressure range suitable for turbine section startup.
 6. The combined cycle power plant startup system of claim 5, wherein the pressure range is about 90 to about 120 pounds per square inch atmospheric.
 7. The combined cycle power plant startup system of claim 1, wherein the bypass system is a first bypass system, further comprising a second bypass system configured to adjust the steam pressure upstream of the reheater by routing steam upstream of the reheater to the first bypass system, the second bypass system comprising at least one bypass line, at least one control valve operably connected to the at least one bypass line, a pressure gauge configured to monitor the steam pressure upstream of the reheater, and a controller configured to communicate with the pressure gauge and regulate the at least one control valve.
 8. The combined cycle power plant startup system of claim 7, wherein the at least one bypass line is a plurality of bypass lines, wherein the at least one control valve is a plurality of control valves, and wherein the controller is configured to communicate with the pressure gauge and operate the plurality of control valves in sequence.
 9. The combined cycle power plant startup system of claim 8, wherein operating the plurality of control valves in sequence comprises opening a plurality of control valves when steam upstream of the reheater reaches a fixed pressure limit, setting a first control valve to auto-control, and setting a second control valve to auto-control when the first control valve reaches a fixed valve stroke limit.
 10. The combined cycle power plant startup system of claim 9, wherein the fixed pressure limit is about 130 pounds per square inch atmospheric.
 11. The combined cycle power plant startup system of claim 9, wherein the fixed valve stroke limit is about 90%.
 12. A combined cycle power plant startup system comprising: a steam turbine, the steam turbine comprising an intermediate pressure turbine; a heat recovery steam generator operably connected to the steam turbine for providing steam to the steam turbine, the heat recovery steam generator comprising a reheater; a condenser; an intermediate pressure bypass system configured to route steam downstream of the reheater to the condenser, the intermediate pressure bypass system comprising a plurality of bypass lines, a plurality of control valves, a pressure gauge configured to monitor the steam pressure downstream of the reheater, and a controller programmed to communicate with the pressure gauge and operate the plurality of control valves in sequence, wherein operating the plurality of control valves in sequence comprises opening the plurality of control valves when steam downstream of the reheater reaches a fixed pressure limit, setting a first control valve to auto-control, and setting a second control valve to auto-control when the first control valve reaches a fixed valve stroke limit, and wherein setting one of the first control valve or the second control valve to auto-control comprises setting the control valve to an adjustable stroke setting, such that a stroke of the control valve automatically adjusts in order to adjust or maintain the pressure of steam downstream of the reheater at a pressure range suitable for admission to the intermediate pressure turbine; and a high pressure bypass system configured to route steam upstream of the reheater to the intermediate pressure bypass system, the high pressure bypass system comprising a plurality of bypass lines, a plurality of control valves, a pressure gauge configured to monitor the steam pressure upstream of the reheater, and a controller configured to communicate with the pressure gauge and operate the plurality of control valves in sequence, the steam pressure downstream of the reheater being adjusted to a pressure range suitable for intermediate pressure turbine startup.
 13. The combined cycle power plant startup system of claim 12, wherein the pressure range is about 90 to about 120 pounds per square inch atmospheric.
 14. The combined cycle power plant startup system of claim 12, wherein the fixed pressure limit is about 120 pounds per square inch atmospheric and the fixed valve stroke limit is about 90%.
 15. The combined cycle power plant startup system of claim 12, wherein regulating the plurality of high pressure bypass system control valves comprises opening the control valves when steam upstream of the reheater reaches a fixed pressure limit, setting a first control valve to auto-control, and setting a second control valve to auto-control when the first control valve reaches a fixed valve stroke limit.
 16. The combined cycle power plant startup system of claim 15, wherein the fixed pressure limit is about 130 pounds per square inch atmospheric and the fixed valve stroke limit is about 90%. 